[RISCV][CostModel] Remove cost of icmp inst in icmp+select with SFB. (#91158)

With ShortFowrardBranchOpt(SFB) or ConditionalMoveFusion, scalar
ICmp and scalar Select instructions will lower to SELECT_CC
and lower to PseudoCCMOVGPR which will generate a conditional
branch instruction and a move instruction.
The cost of scalar (ICmp + Select) = (0 + Select instruction cost)